The invention relates to the manufacture of corrugated tubes and more particularly to the shaping of such tubes by hammering. The invention more particularly is directed to providing a method and a device for shaping by hammering a tube so as to impart thereto in particular a corrugated configuration, and to the application of such a tube in for example, the automobile industry.
As is known, corrugated tubes, whether their cross-section be circular or otherwise and the corrugations be helical or otherwise, are used in different fields in industry.
For example, there are employed such tubes which have a certain flexibility in both the axial and transverse directions for absorbing differences in alignment or expansions of tubular pipes subjected to thermal stresses or mechanical stresses such as vibrations. Such tubes compensate for the longitudinal expansions and/or take into account defects in the axial alignment between different pipes located on each side of the corrugated tube section.
Another application in the automotive field consists in using the tube for absorbing energy developed by the driver who is thrown forward as a result of a relatively violent front collision; the driver, by a return shock, strikes the driving wheel and there is a risk of the latter producing serious thoracic lesions if it is incapable of at least partly withdrawing under the impact of the driver. This is for example the reason why such corrugated tubes are located immediately behind the steering wheel between the latter and the dashboard, or behind the dashboard between two rigid sections of the upper part of the steering column placed between the mounting of the column on the dashboard and the steering box.
Such applications of corrugated tubes are common. It will therefore be understood that the manufacture of such tubes is of considerable practical interest. At the present time, a currently-employed solution for manufacturing a corrugated tube consists in deforming the tube under the action of a high hydraulic pressure; there is carried out an operation which is usually termed "a hydraulic forming" in the art. An oil pressure is developed within the tube and optionally combined with an axial thrust so as to deform the tube against a female member which has impressions of the corrugations to be obtained. Simultaneously with the inflation of the tube which expands, all the corrugations thus obtained move closer together and thus permit conserving a substantially constant thickness of the metal of the walls of the corrugations. Each outer female part which carries the impression of a corrugation is controlled mechanically or hydraulically.
Such a manufacturing technique, however, presents drawbacks. Indeed, it requires a very complex specific machine which can only form a small number of corrugations in each operational cycle of the machine. Use is made of a pressure developed by the oil and it is difficult to eliminate the residual oil which remains inside the shaped corrugated tube. Furthermore, the profile of the corrugations must be very progressive if good results are to be obtained.
Another solution is that disclosed in the French Pat. Application No. 2 176 707. This document proposes manufacturing corrugated tubes by means of an apparatus which comprises a mandrel carrying on its periphery impressions of the corrugations to be obtained, and a ring arrangement of toothed wheels placed radially therearound with their axes orthogonal to the mandrel axis. These wheels carry on their periphery impressions of the corrugations to be obtained which are complementary to those of the mandrel. The tube to be shaped is placed between the wheels and the mandrel whose impressions interengage in the manner of teeth of gear wheels and thus deform the tube which is advanced in a single axial translation with the mandrel through the ring arrangement of toothed wheels to the exclusion of any rotation which would be disadvantageous.
Another technique resides in the deformation of the tube by hammering. This is achieved by means of hammers which are subjected to reciprocating radial movements relative to the axis of the tube and which come to bear periodically with more or less brutality against the outer periphery of the tube to effect a deformation by hammering. This technique permits obtaining local reductions in the diameter, flat portions and successive narrowings. Sometimes, in some cases, in order to avoid a crushing of the tube under the forces developed by the various hammers, it may be desirable to dispose in the tube a core whose profile corresponds to the profile of the configuration to be given to the tube; this is, for example, employed when manufacturing splined tubes by means of a complementary splined core. For carrying out this technique, there are employed hammers which are disposed equally spaced apart on the periphery of the tube to be shaped and are periodically shifted in a reciprocating manner and in succession for example by means of rollers which circulate in a cage roughly in the manner of a roller bearing.
Depending on the results to be obtained, the dimensions and the type of the tube to be shaped, the number of hammers used rarely exceeds twelve.
As this complex hammering technique is well known, it need not be referred to in more detail. The numerous drawbacks of this technique are also known and are similar to those previously discussed with respect to the hydraulic forming operation.